"Receiving Sleep" on Brother Fax 4100

I just fixed this identical problem: Incoming calls would not wake the fax machine out of sleep mode. The ringer would not ring when a call was incoming, but if I picked up the handset, the call was there. I had a normal dialtone and was able to place outgoing calls. This problem was intermittent -- it seemed to be affected by weather, humidity, outside temperature, etc.

I had to get Qwest out to our site to check the phone line itself. We discovered that the ring generator (telco equipment) on the line was bad.

U.S. phone lines operate on a normal line voltage of 48V. When a call comes in, the ring generator circuit generates a pulse of approximately 40V above the normal line voltage, and that's what causes the ringer on the receiving equipment to activate.

The ring generator on our fax line was only generating a pulse of less than 10 volts above the normal line voltage, which was not enough to be detected as a ring signal.

When the repairman switched the line over to a different circuit with a different ring generator at the telco box outside our facility, the fax machine immediately began working properly and has not been a problem since.

I recommend that you have the phone company use a voltmeter to test the ring generator voltage on your line. If it's faulty, they should replace it at no charge to you as it's telco equipment, not Customer Premise Equipment (CPE).

Hope this helps!